The 66-year-old socialist was once mayor of Venice. In 1987, he was ousted after a battle with opponents of the mobile barriers that are now, after numerous delays, being constructed as part of what is known as Project Moses.

"On that occasion, I said: 'I declare for future memory that if anything irreparable should happen to the city, the guilty should be looked for among those who today have impeded the start of works for its defence.'"

On Monday, something irreparable nearly did happen. Venice was hit by the fourth-worst flood since 1872. Driven by winds powering up the Adriatic, the water in the lagoon surrounding the city rose 156cm (61in) above normal levels.

Yet Laroni was not alone in appealing to posterity. The main opposition group, the Permanent "No Moses" Assembly, said that if it had not been for channels gouged at the lagoon entrance to accommodate the barriers, this week's acqua alta (high water) would have been 20cm lower.

"Who will the younger and future generations turn to if they find out that the project does not give the hoped-for results?" the group asked.

Far from settling the argument over how best to defend beautiful, fragile Venice, this week's flood has revived it.

"In the 1980s, it became political," said Anna Somers Cocks, chairman of the Venice in Peril Fund. "The communists and Greens decided to oppose the barriers on the grounds they were ecologically unsound and intended to make big profits for big business."

The Permanent Assembly proposes a programme of "gradual, experimental and reversible" works that includes making the lagoon shallower. It also wants work resumed on strengthening and raising the city's man-made foundations.

Crucially, the barrier scheme's opponents include Venice's mayor, Massimo Cacciari, who is struggling to run the city on a budget reduced to fund Moses.

With the water still thigh-high in St Mark's Square, Cacciari this week conceded the barriers would shield the city, then added: "Every 23 years" - the period since the last big flood in 1985.

This remark left supporters of the scheme seething with indignation.

"It's not true," said Flavia Faccioli, spokeswoman for the construction consortium. "The barriers are designed to be raised when the water reaches 110cm above normal. In the 10 years from 1996 to 2005, that happened 55 times."

Since 2005, however, there have been relatively few high waters. The case against Project Moses may also have been boosted by the apparent lack of damage during this week's undeniably serious flooding.

But Pietro Bortoluzzi, leader of the rightist National Alliance group on the council, said the archives of the National Library of St Mark's, which include one of the world's greatest collections of classical manuscripts, had been "saved by a whisker".

And Somers Cocks cautioned: "Go around Venice, and look at where the salt crystals are efflorescing on the brickwork and plaster. It is up to the first - in some cases, the second - floor."

Project Moses is due for completion between 2012 and 2014. But there is still no single body responsible for the defence of the city, and no plan for its long-term preservation, let alone funding. "Venice will survive only for as long as man wants it to survive," Somers Cocks warned.